This invention relates to a method of and a device for performing image compression (image coding) and image expansion (image decoding), which are based on lossless wavelet transformations on which attention is focused as a platform of the next-generation image coding system capable of implementing a unified form of lossless coding/lossy coding.
In an image compressing/expanding device constructed based on conventional linear transformations such as a wavelet transformation, DCT, etc., the implementation of the function of progressively reproducing and displaying image data by fewer numbers of execution memories and fewer numbers of arithmetic operations takes advantage of the fact that an inverse wavelet transformation, a DCT inverse transformation or the like is a linear transformation (linear system). Further, since the arithmetic order of operations necessary for the inverse transformation and addition made upon updating information in a transformation coefficient domain is changeable, the order of these is changed, an inverse transformation is effected only on transformation coefficient information necessary for information updating and the so-obtained result is added to the immediately-preceding reconstructed image data in an image domain, whereby the progressive reconstruction display of the image has been realized.
FIG. 1 is a block diagram of an image expanding device which executes a processing order obtained from the changing of the arithmetic order created based on the contents described in, for example, IEEE Data Compression Conference (DCC-96), April 1996 xe2x80x9cFast Reconstruction of Subband Decomposed Signals for Progressive Transmissionxe2x80x9d. In the drawing, pre-updating transformation coefficient information b0 is inversely transformed by an inverse transformer 101 and updated information xcex94b0 is inversely transformed by an inverse transformer 102. Thereafter, the outputs of both inverse transformers are added together by a transformation coefficient information updater 103 to thereby obtain a reconstructed image (b0+xcex94b0) 104.
In the progressive reconstruction display of the image by the image compressing/expanding device based on the conventional linear transformations as described above, the inverse transformation is effected only on the transformation coefficient information necessary for information updating by using the linearity of the transformation. The so-obtained result is added to the immediately preceding reconstructed image. Thus, the progressive reconstruction display of the image can be implemented without additionally holding information about transformation coefficients used to reconstruct the immediately preceding reconstructed image. As a result, execution memories could be reduced in number.
Further, the speeding up of processing can be implemented by utilizing a property of the coefficients whose values are zero, increase the number and omitting inverse transformation arithmetic operations on these coefficients when data is reconstructed only from the transformation coefficients necessary for updating.
However, an image compressing/expanding device based on conventional linear transformations has the problem in that a high picture-quality reconstructed image having the image quality of strictly the same level as the original image cannot be obtained due to a quantization error or the like.
While the image compressing/expanding device based on the lossless wavelet transformation can obtain the high picture-quality reconstructed image, the inverse lossless wavelet transformation used as the platform of the image expanding device includes a non-linear arithmetic operation. Therefore, the progressive reconstruction display of the image must be inevitably implemented by updating information in a wavelet transformation coefficient domain and thereafter performing an inverse lossless wavelet transformation on it in order to implement the progressive reconstruction display of the image. Thus, the lossless wavelet transformation coefficients used to generate the pre-updating image, i.e., all the information immediately before the execution of the inverse lossless wavelet transformation must be held to update the displayed image. Therefore, a problem arises in that the size of the execution memory is reduced and a high-speed image progressive reconstruction display cannot be implemented.
Further, a problem arises in that since the number of transformation coefficients zero in value relatively increases if an inverse lossless wavelet transformation is effected on wavelet transformation coefficients comprised of only information necessary for updating, it is quite natural that the number of arithmetic operations at the inverse lossless wavelet transformation can be reduced and the processing can be speeded up by using its relative increase, but the number of the transformation coefficients zero in value relatively decreases because the inverse lossless wavelet transformation is made after the updating of information in a transformation coefficient domain. Thus the speeding up of the processing utilizing the property that many coefficients zero in value are included in the wavelet transformation coefficients indicative of the information necessary for updating cannot be expected. Namely, the image compressing/expanding device based on the linear transformation and the image compressing/expanding device based on the lossless wavelet transformation have both merits and demerits respectively.
With the foregoing problems in view, it is therefore an object of the present invention to provide an image compressing/expanding device based on a lossless wavelet transformation/inverse transformation, which is capable of implementing a progressive reconstruction display of an image while limiting or controlling the consumption of execution memories, thereby obtaining a high picture-quality reconstructed image.
An image compressing/expanding method according to the invention as claimed in claim 1 comprises, on the image compression side, performing quantization and entropy coding on a lossless wavelet transformation coefficient subjected to a lossless wavelet transformation, and on the image expansion side, adding pre-quantization data generated when an inverse lossless wavelet transformation is effected on a lossless wavelet transformation coefficient subjected to entropy decoding and inverse quantization to thereby generate an image, to the next updated data subjected to entropy decoding and inverse quantization, and thereafter performing the inverse lossless wavelet transformation on the result of addition.
Owing to such a construction, the image compressing/expanding method based on the lossless wavelet transformation brings about an effect in that a progressive representation can be implemented and a high picture-quality reconstructed image having image quality of strictly the same level as the original image can be obtained.
An image compressing/expanding method according to the invention as claimed in claim 2 comprises, on the image compression side, performing quantization and entropy coding on each lossless wavelet transformation coefficient subjected a lossless wavelet transformation, and on the image expansion side, effecting an inverse lossless wavelet transformation on each lossless wavelet transformation coefficient subjected to entropy decoding and inverse quantization to thereby generate an image, and generating updated auxiliary information necessary upon updating an image by adding the image generated by the inverse lossless wavelet transformation to the already generated image, from information necessary upon updating the quality of the image by one stage and some of information about each transformation coefficient immediately before the execution of the inverse lossless wavelet transformation.
Owing to such a construction, an effect is brought about in that upon implementation of a progressive reconstruction display, it is unnecessary to hold all the transformation coefficient information used to generate a pre-updating image and an execution memory can be reduced in size.
An image compressing/expanding device according to the invention as claimed in claim 3 comprises
an image compressing device including a lossless wavelet transformation unit for subjecting a digital image to a lossless wavelet transformation, and a progressive coding generation unit for subjecting lossless wavelet transformation coefficients obtained as a result of lossless wavelet transformations to quantization and entropy coding to thereby generate a coded bit stream added to an already generated coded bit stream and simultaneously generating a progressive coded bit stream while repeating this operation until the value of a quantization error reaches zero, and
an inverse lossless wavelet transformation unit for effecting an inverse lossless wavelet transformation on each lossless wavelet transformation coefficient subjected to entropy decoding and inverse quantization with each of N types of data necessary to update data of the progressive coded bit stream by N stages as one processing unit, thereby generating an image, a transformation coefficient buffer for holding some of pre-quantization transformation coefficient data generated upon the generation of the image, and a transformation coefficient information updater for adding updated auxiliary information generated from data obtained by subjecting transformation coefficient data obtained by effecting entropy decoding and inverse quantization on the next processing unit bearing information for updating the image on an inverse lossless wavelet transformation with the inverse lossless wavelet transformation unit, some of the same inversely-transformed data and the data held in the transformation coefficient buffer, to the immediately preceding reconstructed/displayed image in an image domain, thereby to update image information.
Owing to such a construction, the image compressing/expanding method based on the lossless wavelet transformation allows a progressive representation to be implemented and a high picture-quality reconstructed image having image quality of strictly the same level as the original image can be obtained.
An image compressing/expanding device according to the invention as claimed in claim 4 comprises
an image compressing device including a lossless wavelet transformation unit for subjecting a digital image to a lossless wavelet transformation, and a progressive coding generation unit for subjecting lossless wavelet transformation coefficients obtained as a result of lossless wavelet transformations to quantization and entropy coding to thereby generate a coded bit stream added to an already generated coded bit stream and simultaneously generating a progressive coded bit stream while repeating this operation until the value of a quantization error reaches zero, and
an image expanding device including an inverse lossless wavelet transformation unit for effecting an inverse lossless wavelet transformation on each lossless wavelet transformation coefficient subjected to entropy decoding and inverse quantization with each of N types of data necessary to update data of the progressive coded bit stream by N stages as one processing unit, thereby generating an image, a transformation coefficient buffer for holding information necessary upon updating the quality of the image by a further stage, of the lossless wavelet transformation coefficients, and an updated auxiliary information generator for generating updated auxiliary information additionally necessary upon updating the image by adding the image generated by the inverse lossless wavelet transformation to the already-reconstructed image from the information stored in the transformation coefficient buffer and information about each transformation coefficient immediately before the execution of the inverse lossless wavelet transformation.
Owing to such a construction, an effect is brought about in that upon implementation of a progressive reconstruction display, it is unnecessary to hold all the transformation coefficient information used to generate a pre-updating image and an execution memory can be reduced in size.
An image compressing/expanding device according to the invention as claimed in claim 5 comprises
an image compressing device having at least one S transformation part for implementing a lossless wavelet transformation by an S transformation, and
an image expanding device having at least one Inverse S transformation part for implementing an inverse lossless wavelet transformation by an inverse S transformation, and wherein the updated auxiliary information is generated only from LSB of respective lossless wavelet S transformation coefficients necessary to generate a pre-updating image through a lossless wavelet inverse S transformation and LSB of lossless wavelet S transformation coefficients bearing only information necessary for updating.
Owing to such a construction, an effect is brought about in that the amount of information about transformation coefficients held to generate updated auxiliary information necessary to implement a progressive reconstruction display can be limited to one bit for each transformation coefficient and the size of an execution memory can be reduced.
An image compressing/expanding device according to the invention as claimed in claim 6 comprises
an image compressing device having at least one TS transformation part for implementing a lossless wavelet transformation by a TS transformation, and
an image expanding device having at least one inverse TS transformation part (constructed by an S transformation and a linear transformation and a non-linear transformation placed in its previous stage) for implementing an inverse lossless wavelet transformation by an inverse TS transformation, and wherein the generation of updated auxiliary information under a progressive reproducing process through an inverse transformation set in a stage preceding an inverse S transformation is performed as a first stage based only on the two rightmost bits of respective transformation coefficients necessary to generate pre-updating data through the same inverse transformation and the two rightmost bits of respective transformation coefficients bearing only information newly necessary for updating, and as a second stage, the so-obtained updated information is progressively reconstructed through the inverse S transformation as an input, whereby the progressive reconstruction display of an image at the image expanding device is performed in accordance with the two-stage processing through the inverse S transformation.
Owing to such a construction, an effect is brought about in that as compared with the case where the S transformation and Inverse S transformation are used, a higher picture-quality reconstructed image can be obtained if compared at the same bit rate.
An image compressing/expanding device according to the invention as claimed in claim 7, is constructed in such a manner that the image compressing device or the image expanding device is provided with an S transformation/TS transformation selector for repeatedly applying band division to the lowest frequency components generated by the lossless wavelet transformation every x and y directions so as to divide into a desired number of bands and selecting the corresponding lossless wavelet transformation so as to selectively use the S and TS transformations according to the respective directions and respective repetitions without always having to use a single transformation.
Owing to such a construction, an effect is brought about in that as compared with the case in which the S transformation and Inverse S transformation are used, a higher picture-quality reconstructed image can be obtained if compared at the same bit rate, and the size of an execution memory can be reduced as compared with the case in which a TS transformation and an inverse TS transformation are used as all the transformations and inverse transformations.
An image compressing/expanding device according to the invention as claimed in claim 8 comprises
an image compressing device including a lossless wavelet transformation unit for subjecting a digital image to a lossless wavelet transformation, and a progressive coding generation unit for subjecting lossless wavelet transformation coefficients obtained as a result of lossless wavelet transformations to quantization and entropy coding to thereby generate a coded bit stream added to an already generated coded bit stream and simultaneously generating a progressive coded bit stream while repeating this operation until the value of a quantization error reaches zero, and
an image expanding device including an inverse lossless wavelet transformation unit for effecting an inverse lossless wavelet transformation on each lossless wavelet transformation coefficient subjected to entropy decoding and inverse quantization with each of N types of data necessary to update data of the progressive coded bit stream by N stages as one processing unit, thereby generating an image, a transformation coefficient buffer for holding information necessary upon updating the quality of the image by a further stage, of the lossless wavelet transformation coefficients, an updated auxiliary information generator for generating updated auxiliary information additionally necessary upon updating the image by adding the image generated by the inverse lossless wavelet transformation to the already-reconstructed image from the information stored in the transformation coefficient buffer and information about each transformation coefficient immediately before the execution of the inverse lossless wavelet transformation, a zero coefficient determinator for determining, immediately before the execution of the inverse lossless wavelet transformation, whether the values of the respective transformation coefficients are zero, and a zero coefficient arithmetic omitter for omitting a sum-of-products arithmetic operation for an inverse lossless wavelet transformation effected on the transformation coefficients whose values are zero.
Owing to such a construction, an effect is brought about in that a progressive reconstruction display process can be speeded up.
An image compressing/expanding device according to the invention as claimed in claim 9 is constructed such that the image expanding device is provided with a zero number counter for counting the number (zero number) of continuously-generated values zero of the transformation coefficients and outputting a signal used to omit the sum-of-products arithmetic operation for the inverse lossless wavelet transformation when the number thereof reaches a predetermined counted value.
Owing to such a construction, an effect is brought about in that a progressive reconstruction display process can be further speeded up.
An image compressing/expanding device according to the invention as claimed in claim 10 is constructed such that the image compressing/expanding device as claimed in any of claims 3 to 9 is applied to an image decoding process of a facsimile.
Owing to this construction, an effect is brought about in that upon the image decoding process of the facsimile, the consumption of execution memories can be reduced and a high picture-quality image can be obtained.
An image compressing/expanding device according to the invention as claimed in claim 11 is constructed such that the image compressing/expanding device as claimed in any of claims 3 to 9 is applied to an image decoding process of a portable information terminal.
Owing to this construction, an effect is brought about in that upon the image decoding process of the portable terminal, the consumption of execution memories can be reduced and a high picture-quality image can be obtained.
An image compressing/expanding device according to the invention as claimed in claim 12 is construction such that the image compressing/expanding device as claimed in any of claims 3 to 9 is applied to an image decoding process of a high image-quality display unit.
Owing to this construction, an effect is brought about in that upon the image decoding process of the high image-quality display unit, the consumption of execution memories can be reduced and a high picture-quality image can be obtained.
An image compressing/expanding device according to the invention as claimed in claim 13 is constructed such that the image compressing/expanding device as claimed in any of claims 3 to 9 is applied to an image decoding process of a printer.
Owing to this construction, an effect is brought about in that upon the image decoding process of the printer, the consumption of execution memories can be reduced and a high picture-quality image can be obtained.